The afferent and efferent connections of the pretectal region will be explored in the rat, cat and monkey, using the autoradiographic and horseradish peroxidase techniques for the tracing of nervous pathways in the brain. BIBLIOGRAPHIC REFERENCES: Coleman, D.R. and Scalia, F. Anterograde transport of HRP in the primary optic pathway of the mouse. Anat. Rec., 181, 526, 1975. Coleman, D.R. and Scalia, F. Light and electron microscopic observations on the anterograde transport of horseradish peroxidase in the optic pathway of the mouse and rat. Brain Res., 102, 156-163, 1976.